The Student Room Group

Shapes of molecules and their names

I understand that SF4 has 4BP and 1LP but I don't understand why it's called a trigonal pyramidal because I thought that trigonal pyramidal must have 3BP and 1LP. Also, I don't understand why the angle is 119⁰ and 89⁰
Original post by Bird1234
I understand that SF4 has 4BP and 1LP but I don't understand why it's called a trigonal pyramidal because I thought that trigonal pyramidal must have 3BP and 1LP. Also, I don't understand why the angle is 119⁰ and 89⁰

The atoms are arranged in a see saw (saw horse) arrangement. The central sulfur atom is at the apex of two trigonal pyramids. It is trigonal bipyramidal
(edited 6 months ago)
Reply 2
Original post by charco
The atoms are arranged in a see saw (saw horse) arrangement. The central sulfur atom is at the apex of two trigonal pyramids. It is trigonal bipyramidal

OK thank you I now understand the name but would the angle be 90 and 120 or would the lone pair affect the angle
Original post by Bird1234
OK thank you I now understand the name but would the angle be 90 and 120 or would the lone pair affect the angle

No, the trigonal pyramids are not regular. The lone pair of course affects the bonding pairs.
There is a whole page on it here: https://geometryofmolecules.com/sf4-lewis-structure-polarity/
Reply 4
Original post by charco
No, the trigonal pyramids are not regular. The lone pair of course affects the bonding pairs.
There is a whole page on it here: https://geometryofmolecules.com/sf4-lewis-structure-polarity/

OK thanks
Reply 5

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